Process of preparing homogeneous solutions of cellulose in acids, and of preparing artificial products therefrom



Patented Mar. 24, 1936 T SOLUTIONS OF CELLULOSE IN ACIDS, AND OF PREPARING ARTIFICIAL PRODUCTS THEREFROM Jan Cornelis de Nooij, The Hague, and Dirk Jan Gerritsen, Arnhem, Netherlands No Drawing. Application November 14, 1934, Serial No. 753,064. In Germany April 24., 1933 3 Claims.

When preparing artificial silk from solutions of cellulose in sulphuric and other acids suitable for the production of artificial threads, films, ribbons and such like artificial products, the difiiculty is encountered that the solution contains a greater or smaller amount of undissolved particles which are not easily removed even by filtration.

According to the invention the cellulose is first converted into a homogeneous suspension of fibres before the dissolving takes place, in order to avoid the difliculty referred to above, the conversion being efiected by treating the cellulose for a short time with a sufiicient quantity of acid of alower concentration than is necessary for dissolving the cellulose and which destroys the mutual connections of the cellulose fibres to form the aforesaid suspension. p

In the cellulose-sulphuric acid process, the cellulose may be treated with sulphuric acid of about 57-63%, this strength of acid being insufiicient to efiect solution of the cellulose, and then further sulphuric acid is quickly added to the pre-treated cellulose with stirring or kneading, the quantity and concentration of the sulphuric acid being such that the cellulose in suspension dissolves. The dissolving acid should be added very quickly, as already mentioned, so that it is well mixed in with the fibre suspension before" the cellulose becomes colloidal.

The suspension-forming pre-treatment may be carried out with about ten parts of sulphuric acid to one of the cellulose.

In order that the invention may be clearly understood the following example is given. To air-dray sheets of sulphate-cellulose the ten-fold quantity of sulphuric acid of 60% at 15 C. is added. Almost directly the mutual connections between the cellulose fibres are broken up so that a suspension of fibres is formed without the cellulose being dissolved. The porridge-like mass prepared in this way is stirred in a kneading-machine for a very short time in order to ensure that the suspension of fibres is homogeneous. Thereupon the dissolving-acid is added quickly with continued kneading or stirring and in such quantity that the concentration, disregarding the cellulose, is 63%. Almost immediately the solution becomes absolutely homogeneous and free from fibres, and may be spun in the known way, after being subjected to some further treatment, if desired, such as one for rendering the solution metastable.

It has been found that, dependent on the quality of the cellulose and the temperature, with a (Cl. 260-) V concentration of sulphuric acid less than 60-57%,

the mutual connections of the cellulose fibres are not to be destroyed so that in such cases a suspension of fibres can only be obtained by me chanical means. If the suspension-acid. is at a lower temperature, the suspension is 'formed at a lower concentration. however, there is a corresponding concentration For every temperature of the suspension-acid, for instance it has been it will not be possible to prepare an absolutely homogeneous solution within a reasonably short time.

As stated above, the concentration of the acid used to form the suspension is dependent on the kindof cellulose employed. Some kinds have a higher dissolving point than others, andthe point at which the suspension is formed, rises accordingly. There exists a certain variety of linters (for example, those made by Temming, of Hamburg) which dissolves at 66%. In this case 63% is a particularly useful concentration to form the suspension.

The new process has the following advantages:

1. Byno other methodcan a completely homogeneous solution be obtained. However, by first of all preparing, according to the invention, a suspension of fibre, a perfect, absolutely homogeneous solution is formed in an efiicient manner as in this process it is prevented that the particles of cellulose are not wetted at all, or not wholly wetted, by the dissolving-acid.

2. In applying the process according to the invention the dissolving can be carried out by means of the theoretical minimum concentration of the sulphuric-acid, that is, the minimum concentration of sulphuric acid by which the individual fibres are colloidally dissolved may be used in carrying out the process on a commercial scale. For instance, when using a final sulphuric acid concentration of 63% .by weight (disregarding the cellulose) it is possible to prepare good solutions of the cellulose, this being impossible if the process according to the invention is not applied.

3. The preparation of the suspension and also the solution require a few minutes only, which is a great'economical advantage, very important for instance for the quality of the final product, because as long as a solution is not metastabilized, the cellulose of the solution saccharifies. v

4. The preparation of the solution can be carried out by means of the most simple apparatus.

5. The process according to the invention enables the preparation of a solution the percentage of cellulose in which is as high as possible, the solution not being rendered non-homogeneous nor containing undissolved particles.

When carrying out the researches which have led to the present invention it has ben found that other means do not lead to the desired result. For instance attempts have been made to produce a homogeneous solution by spraying the loosened cellulose material with the dissolving acid. Undissolved particles however remained in the solution, and the viscosity of the solution varied locally. The same difiiculties Occurred if the cellulose was pre-treated with acid which does not break up the mutual connections of the cellulose fibres. Even finely dividing the mass into so-called crumbs in a crumblingmill did not give better results.

Therefore, the invention gives unexpected and commercially important results, and is based on the conception of founding the process on a suspension of fibres and of utilizing the difiierent concentrations of the acid, namely that concentration of acid by which the mutual connections of the cellulose fibres are destroyed, (to form the suspension) and that concentration of acid by which the cellulose is dissolved. This suspension method may be used for all other direct cellulose-dissolving acids, as for instance hydrochloric acid, phosphoric acid and so on, or mixture of acids such as f. i. a mixture of sulphuric acid and hydrochloric acid.

As already stated, it has been found that this suspension method is the only method of preparing absolutely homogeneous solutions of cellulose in acids, in consequence of the, in general, very quick dissolving properties of the acids. When the fibres are not dissolved at the same time from all sides, which is the case when the cellulose is first divided into crumbs", then the crumbs are partially dissolved at the outside, before the dissolving acid had reached the inside of the crumbs. In consequence of the high viscosity of the solution formed around the inside of the crumbs, the dissolving acid is incapable of reaching the insides of the "crumbs, so that homogeneous solution is impossible.

We claim:-

1. Process of preparing homogeneous solutions of cellulose in acid selected from the group consisting of sulphuric, hydrochloric, and phosphoric acids and mixtures thereof, for the preparation of artificial threads, films, ribbons, and such like artificial products, therefrom, which comprises first converting the cellulose into a homogeneous suspension of fibres, by treating the cellulose for a short time with a sufiicient quantity of such acid of a concentration below the dissolving concentration and which destroys the mutual conthe suspension by adding sulphuric acid in such quantity and of such strength that the dissolving concentration is reached.

DIRK JAN GERRITSEN. JAN CORNELIS DE NOOIJ. 

